1. Field of the Invention
The invention relates to a hydraulic transaxle incorporating a pair of hydraulic motors for respective left and right wheels. The invention also relates to a four-wheel driving vehicle equipped with the hydraulic transaxle incorporating the pair of hydraulic motors and another hydraulic transaxle incorporating a hydraulic motor for driving corresponding left and right wheels, wherein all the hydraulic motors of the two transaxles are driven by a common hydraulic pump.
2. Related Art
Conventionally, there is a conventional well-known transaxle such as disclosed in Japanese Laid Open Gazette No. 2004-210215. The transaxle incorporates a pair of hydraulic motors for driving respective axles (drive wheels), and the hydraulic motors are fluidly connected in parallel to a hydraulic pump out of the transaxle, whereby the wheels driven by the respective hydraulic motors can rotate differentially.
The transaxle incorporating the pair of hydraulic motors instead of a conventional mechanical differential gearing assembly is compact vertically and widthwise so that the vertical position of the transaxle can be optionally lowered so as to stabilize a vehicle or raised so as to ensure a large ground clearance.
The problem of the pair of hydraulic motors fluidly connected in parallel to the hydraulic pump is that, when a vehicle is stuck because one of the wheels driven by the pair of hydraulic motors is caught in a ditch or mud and intends to run idle, fluid from the hydraulic pump is concentrated to the hydraulic motor for driving the idling wheel and the other hydraulic motor is insufficiently supplied with fluid to drive the corresponding wheel. A conventional differential locking system for a conventional mechanical differential gearing assembly, such as disclosed in Japanese Laid Open Gazette No. 2002-22007, does not solve the above problem for the hydraulic transaxle.